Polyurethanes are a known class of materials that have found extensive commercial application because of their excellent physical properties. These polymers are suitable for molding, spraying, and coating products where tensile strength, toughness, and impact resistance are required. In many of the established manufacturing processes it is preferred to employ a one-shot system whereby the polyisocyanate and active hydrogen compounds are converted to the final product in a single reaction step. In other known processes an intermediate product, usually called a prepolymer, is formed first by reacting a stoichiometric excess of a polyisocyanate with an active hydrogen compound, and the prepolymer is subsequently converted to the final polymer in a second reaction involving a further active hydrogen compound, commonly called a chain extender or curing agent.
An example of polyurethane chemistry is disclosed in U.S. Pat. No. 4,933,416 to Gillis, which teaches the use of prepolymers to make polyurethane polymers using isocyanate, a polyol having an average nominal hydroxyl functionality greater than 2 and an average hydroxyl equivalent weight of from about 500 to about 5,000 and polymeric polyamine having an average nominal primary and/or secondary amino functionality of from about 2 to about 3 and an average amine equivalent weight of from about 500 to about 5000. However, this prior art exemplifies the use of only aromatic isocyanates, and restricts the hydroxyl [—OH] equivalent weight of the polyol to be used to be higher than about 500. Moreover, Gillis teaches that if the prepolymer is made by utilizing just one active hydrogen compound, that compound is a trifunctional one.
U.S. Pat. No. 4,443,563 to Dirlikoff et al. discloses the use of dianhydrohexitol as an active hydrogen compound in the preparation of polyurethane; however, this reference teaches making the polymer in a one step process via solution polymerization and subsequent precipitation into an non-organic solvent (for the polyurethane). Such a process is undesirable since the polyurethane must be separated from the solvent to be used.
U.S. Pat. No. 4,564,645 to Salzburg et al. teaches the use of dianhydrohexitol in the preparation of a polyurethane; however it specifies a specific ratio of three isomers of dianhydrohexitol needed to yield a liquid product. The polyurethanes are prepared by reacting an organic polyisocyanate with a compound containing at least two active hydrogen atoms and having a molecular weight of from 400 to 10,000, a chain-extending agent, optionally other short-chain compounds containing at least two active hydrogen atoms and having a molecular weight of from 32 to 399. The chain-extending agent used is a liquid isomer mixture of 1,4-3,6-dianhydrohexitols, preferably 1,4-3,6-dianhydro-D-sorbitol and/or 1,4-3,6-dianhydro-D-mannitol in addition to isomer mixtures containing 1,4-3,6-dianhydroiditol. Additionally, it states that if a prepolymer process is used, the percentage NCO-content of the prepolymer must be between 1 and 18 wt % and preferably 3 to 16 wt %. These mixtures may be used in admixture with low molecular weight compounds preferably polyols having a molecular weight in the range from 62 to 250.